There are a total of 21 rare dwellers.
I'll start with mine. Came free from starting lunchbox.
Sarah Lyons lvl 28 S8 P6 E8 C6 I5 A5 L2
T51f Power Armor adds S2 P5
Wazer Wifle Dmg 12-17
PS: She can explore the wasteland for days.
I dont recall the stats but i had scribe rothchild and he was pretty strong as well and could stay in the wasteland for days before needing to return.
So far I've got 4, playing on 2 different devices, don't recall the original stats, they've leveled up.
Lucas Simms, Amata, Alistair Tenpenny & Three Dog. They all have high everything. You can stick them in pretty much any room and they'll help. I tend to have them reproduce with as many other dwellers as possible. Their offspring sometimes have better traits.
There's lots of other special characters that show up too, some I recognize, but I guess they aren't considered rare.